1. Field of the Invention
The present invention relates to tantalum-amido precursors useful in depositing Ta-containing material on a substrate, e.g., thin film layers of tantalum nitride or tantalum oxide, as well as to the synthesis of such precursors and to deposition methods employing same.
2. Description of the Related Art
Copper is of great interest for use in metallization of VLSI microelectronic devices because of its low resistivity and contact resistance, as well as its ability to enhance device performance (relative to aluminum metallization) by reducing RC time delays and thereby yielding faster microelectronic devices. Copper chemical vapor deposition (CVD) processes useful in large-scale manufacturing of microelectronic devices, e.g., in conformal filling of high aspect ratio inter-level vias in high density integrated circuits, are actively being developed and implemented by the electronics industry.
Although Cu CVD has enjoyed progressively wider usage in semiconductor manufacturing, various problems have resisted solution in the integration of copper in such microelectronic device applications. It is well established that copper diffuses relatively rapidly through many materials, including both metals and dielectrics, especially at temperatures above ˜300° C., resulting in degradation of device performance and reliability, in some instances to the point of inoperability of the microelectronic device.
To inhibit diffusion of copper in microelectronic devices, barrier materials have been developed that separate copper metallization regions from vulnerable device regions, to ensure the long-term reliability of the copper-based metallurgy in integrated circuits (IC). Effective barrier materials generally must possess several characteristics, including a low diffusion coefficient for copper, low electrical resistivity, good thermal stability, effective adhesive interfaces, and the ability to form good nucleation surfaces to promote <111> texture in the deposited copper layer.
To achieve effective barrier performance, deposition of the barrier material desirably involves good step coverage in high-aspect-ratio device features, e.g., dual-damascene trench and via structures. With progressively increasing shrinkage of feature sizes in computer chips, CVD and atomic layer deposition (ALD) of the barrier material have proved advantageous over sputtering and physical vapor deposition (PVD) in achieving uniform-thickness conformal thin films with good step coverage in high-aspect ratio device features.
TaN and TaSiN have been demonstrated as suitable metal diffusion barrier materials. CVD of TaN is currently carried out using Ta(NMe2)5, penta(dimethylamino)tantalum (PDMAT). PDMAT is a solid source precursor that decomposes above 80° C. and has a limited volatility. As such, sublimation is necessary to deposit high purity tantalum-containing films, resulting in increased deposition system complexity and costs, relative to CVD utilizing liquid-phase source reagents.
Ta(NEt2)5, penta(diethylamino)tantalum (PDEAT) is a liquid, but it is unstable under elevated temperature conditions, readily decomposing to a tantalum imide species, Ta(=NEt)(NEt2)3, upon heating and therefore, unsatisfactory as a liquid source reagent for TaN barrier layer formation.
t-BuN=Ta(NEt2)3, tert-butylimino-tris-(diethylamino)tantalum (TBTDET) is a liquid at room temperature and has been proposed as a precursor for depositing TaN, but it has various unfavorable characteristics that limit its utility. Chief among these is the fact that deposition temperatures higher than 600° C. are needed to deposit suitably low resistivity films. Another problem with TBTDET is that too much carbon is incorporated in the deposited tantalum-containing film, and the resulting high carbon layers are highly resistive, and have low density and reduced effectiveness as diffusional barriers.
TaSiN has been proposed as a diffusion barrier material. CVD processes for the formation of this ternary barrier layer material have been the focus of associated development efforts. CVD of TaSiN has been carried out using PDMAT as the tantalum source and silane as the silicon source. TaCl5 in combination with silane and ammonia also has been used for forming TaSiN films. Apart from hazards associated with handling pyrophoric gases such as silane, such approaches require dual source reactor configurations to accommodate the multiple precursor species (TaCl5 or Ta(NMe2)5 as the tantalum reagent and silane as the silicon source). The use of dual source reactor configurations in turn significantly increases the cost and complexity of the semiconductor manufacturing operation, relative to the use of a single source reagent.
In all instances, the formation of a Ta-based diffusion barrier by chemical vapor deposition requires an effective CVD approach. The CVD process must achieve conformal coating of inter-level (<0.15 μm) vias and sidewall. Additionally, the CVD source reagent must be storage-stable, of appropriate volatility and vaporization characteristics, with good transport and deposition characteristics for production of high-purity, electronic quality thin films. CVD source reagents for such purpose are desirably liquid in character, to facilitate liquid delivery techniques that are consistent with effective volatilization and transport of the precursor vapor and the achievement of superior conformal films on the substrate.
Among various chemical vapor deposition techniques, atomic layer deposition (ALD) has emerged in recent years as a promising candidate for deposition of thin films in device structures with very small feature dimensions. ALD is carried out to achieve successive single-monolayer depositions, in which each separate deposition step theoretically goes to saturation at a single molecular or atomic monolayer thickness and self-terminates when the monolayer formation occurs on the surface of the substrate. Single-monolayer depositions are performed a number of times until a sufficiently thick film has been deposited on the substrate.
It would therefore be a significant advance in the art to provide tantalum precursors that are readily synthesized and suitable for use in vapor deposition processes such as ALD or other CVD techiques, that are robust, that possess good volatilization, transport and deposition characteristics, that are amenable to liquid delivery, e.g., by bubbling or direct liquid injection, and that produce tantalum-containing films such as TaN, Ta2O5, TaSiN and BiTaO4, as well as other Ta-nitride and Ta-oxide films, of superior quality and performance characteristics.